This invention relates to the field of electronic communications counter measures, and more particularly to the field of measurement of the effectiveness of jamming upon any given communications link. The methods conventionally used to provide a measure of jamming effectiveness such as the various scoring methods, suffer from a lack of standardization, accuracy, and need for large amount of personnel, cost and time. The lack of standardization in the existing scoring technique is coumpounded by the factors of often using different test messages, different listeners and of having different scoring methods. Types of jamming modulation systems sought to be effectively compared but for which an adequate comparison means was not available by the conventional scoring techniques were: FM by noise, AM by noise, pseudorandom (PN) binary noise, or tone bagpipes. Different test messages used as scoring techniques included the Modified Rhyme Test Message (MRT), the Phonetically Balanced Word List (PBWL), numbers, news broadcasts, and military phrases. The scoring methods were based on either the number of correct listener identified words or on the time required to acknowledge a correct message. These factors affected the determination of the figure of merit for jamming, i.e., the jamming-to-signal (J/S) ratio, which is needed to compare different jamming effectiveness. A standard is needed to facilitate comparison of jamming for systems of different form and structure. Word score tests run on an FM transceiver with different word messages illustrate the difficulties encountered in comparison; and an indication of the imprecise results obtained in any case.
While the J/S ratio, type of jamming modulation, and transceiver link were identical in two instances, a word score was obtained of 20% for a MRT message, but 50% for a PBWL message. While each percentage score may well be indicative of the J/S ratio of the jamming being applied against the link, it is noteworthy that the scores are not capable of ready comparison with each other. Still different results occur with other messages, such as number sequences, or news broadcasts. Consistent scores from a test panel, with any of these techniques requires, additionally, selection of proper listeners, facilities, and a training period. Scoring techniques through mechanizable on a limited basis, nonetheless require costly personnel or equipment. A description is given of the complex scoring method by a trained listener panel using the PWBL, being a conventional approach: A listener test facility consists of eight booths with CRT screens mounted in front of each listener. Fifty words are displayed on the screen and there is a button below each word. Half the words on the screen are correct and the other half are not. The listener is supposed to push the button under the word that he thought he or she heard. A monitor sits in the room and a display in front of him indicates how many correct words each listener has identified. In this way a seasoned group of listeners may be selected who have a good record of accurately identifying a message. Using the same group, a percentage of accurate receipt of a preselected message transmitted through the link, is formed, which is indicative of the jamming to signal ratio in the link. A listener panel with proper facilities and training is required to obtain consistent scores with test messages. The need for assembling such a panel could delay scoring by days or weeks. An alternate approach is mechanized scoring, but present automatic scoring machines are not only costly, but limited in scope. The replacement of these incompatible, laborious and undependable conventional techniques with a rapid, standardized machine-implemented method is therefore readily appreciated.